Tacky rubberlike compositions and method of making the same



l atented Sept. 17, 1946 TACKY RUBBERLIKE COMPOSITIONS AND METHOD OF MAKING THE SAME Robert R. Dreisbach, Edgar C. Britton, and

' Walter J. Le Fevre, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Michigan No Drawing. Application July 16, 1943, Serial No. 495,028

8 Claims.

This invention concerns a method whereby certain rubber-like polymeric products which are non-tacky, or substantially so, may be rendered tacky by treatment with substances which are themselves rubbery and vulcanizable. It also concerns the resultant tacky rubber-like composi tions and the non-tacky rubbery products obtained by vulcanizing the same.

Non-tacky rubber-like polymeric products which may be given tack in accordance with the invention are the subject matter of a co pending application of R. R. Dreisbach, Serial No. 423,295, filed December 17, 1941. They are copolymers of an aliphatic conjugated diolefine, a Z-aryl-lalkene and an alpha-beta unsaturated ketone having the general formula:

R( }--C=CH2 wherein R represents an alkyl radical and R represents hydrogen or an alkyl radical. The nontacky rubber-like products are preferably prepared by polymerizing together between 37 and 65 per cent by weight of an aliphatic conjugated diolefine, between and 60 per cent of such ketone and between 1 and 30 per cent of a 2-aryll-alkene, since, when vulcanized, the products of this composition are highly resistant to abrasion. However, the starting materials may be co-polymerized in other proportions to obtain non-tacky rubbery co-polymers which may be rendered tacky by the present method. Examples of aliphatic conjugated diolefines which may be employed in the polymerization reaction are butadiene-1.3, isoprene and 2.3-dimethyl-butadiene- 1.3, etc. Among the various unsaturated ketoncs which may be employed as starting materials are methyl vinyl ketone, ethyl vinyl ketone, isopropyl vinyl ketone, methyl isopropenyl ketone, ethyl isopropenyl ketone, etc. Examples of 2-aryl-1- alkenes which may be used in preparing the nontacky co-polymers are styrene, alpha-methylstyrene, para-chloro-styrene, ortho-chloro-styrene, para-methyl-styrene, para-methyl-alphamethyl-styrene, ortho-ethyl-styrene and metaethyl-styrene, etc. Any set of these three types of polymerizable compounds may be used in making the non-tacky rubber-like co-polymers.

The (ac-polymerization reaction may be carried out in any of the usual ways, e. g. in the presence or absence of solvents or liquid diluents, but it is advantageously carried out in an aqueous emulsion of the polymerizable compounds and a minor amount of a peroxide catalyst. As the peroxide catalyst, a persulphate, e. g. ammonium, sodium, or potassiumpersulphate, is preferably used, but other peroxides such as hydrogen peroxide, or so dium peroxide, etc., may be employed. The peroxide is usually employed in a proportion corresponding to between 0.5 and 2 per cent of thecombined weight of the polymerizable compounds, but it may be used in other proportions if desired. The emulsion is usually prepared so as to contain a total of from 10 to 50, preferably from 35 to 48, per cent of the polymerizable compounds and the peroxide in the proportion just mentioned. A small proportion of an alkali, e. g. sodium or potassium carbonate or a corresponding hydroxide, is usually added to render the mixture somewhat alkaline. Any of a variety of wellknown emulsifying agents, e. g. the alkali metal sulphonates of aliphatic or alkyl aromatic hydrocarbons of high molecular weight, may be used in preparing the emulsion.

The emulsion is warmed in a closed container to a temperature between 30 and 100 C., pref erably between 50 and C., to efiect the polymerization. The reaction is substantially cornplete after from 10 hours to 3 days of heating.

The co-polymer product may be recovered from the emulsion in any of the usual ways, e. g. :by freezing or by adding coagulating agents such as acids or water-soluble salts, etc. In practiceit is usually coagulated by adding an aqueous solution of calcium chloride or barium chloride. The product is Washed. with water and dried, preferably under vacuum.

The non-tacky rubber-like product thus obtained is readily compounded with carbon black, sulphur, accelerating agents, fillers and other usual rubber-compounding agents and cured to obtain a vulcanized rubbery product having good mechanical properties, e. g. a high tensile strength, good elasticity, and a high per cent elongation value before breakage occurs, etc., and which is exceptionally resistant to wear by abrasion. However, due to the fact that the uncured co-polymer possesses little or no tackiness, it does not adhere well to the fabrics, e. g. of cotton or rayon, which are used in the construction of tires, hoses, rubber belting, etc.

Treatment of the uncured co-polymer with organic resins or plasticizing agents such as are sometimes used to render other kinds of rubber tacky, usually either fails to impart tackiness to the co-polymer, or weakens or otherwise impairs its quality. Such resins and plasticizers are in most, if not all, instances non-rubbery materials which cannot be vulcanized. The incorporation of such substances in a rubber amounts to diluting the latter.

According to the present invention, such nontacky rubber-like co-polymer of a conjugated diolefine, a 2-aryl-1-alkene and an unsaturated ketone is rendered tacky by incorporating therewith between 5 and 25, and preferably between 8 and. 20, per cent by weight of a tacky co-polymer of a diolefine, a 2-aryl-1-alkene and an unsaturated ketone having the general formula herein- 3 befor mentioned, which tacky co-polymer may be prepared as described in a co-pending application of E. C. Britton and W. J. LeFevre, Serial No. 494,922, filed concurrently herewith. Peculiarly, although the non-tacky type of co-polymer may be rendered tacky by mixing from to 25 per cent of the tacky co-polymer therewith, the addition of a larger proportion of the tacky co-polymer often fails to yield a tacky mixture. Also, the use of more than 25 per cent of the tacky co-polymer may result in weakening of the vulcanized rubbery mixture. It should be mentioned that the tacky type of co-polymer is itself somewhat rubbery and that it may be vulcanized to produce a rubber-like product. Accordingly, incorporation of the tacky type of co-polymer with the non-tacky co-polymer does not involve dilution of the final rubbery product.

The tacky type of co-polymers preferably employed in the process are those composed of from 37 to 65 per cent by Weight of an aliphatic conjugated diolefine, from 20 to 60 per cent of an unsaturated ketone and from 1 to 30 per cent of a Z-aryl-l-alkene. However, tacky co-polymers of such polymerizable compounds in other proportions may, in some instances, be used. EX- amples of a number of diolefines, unsaturated ketones and Z-aryl-l-alkenes which may be used in preparing the tacky co-polymers have hereinbefore been given with reference to thepreparation of the non-tacky type of co-polymer and need not be repeated. The tackiness of a co-polymer is dependent, not only on its composition, but also upon the conditions under which it is prepared.

In preparing the tacky type of co-polymer, the above-mentioned polymerizable compounds in th proportions stated are polymerized while in an aqueous emulsion which is of a pH value below 3 and which contains an iron salt, e. g. ferric 4 chloride, ferric nitrate, ferric sulphate, or ferric acetate, etc., and which also contains a, peroxide throughout the major portion, and preferably the entire, reaction period. The ferric salt need not be added as such, but may be formed in situ, e. g. by oxidation of a corresponding ferrous salt. Hydrogen peroxide is preferably used as the peroxide ingredient of the mixture, but other peroxides, e. g. sodium peroxide, barium peroxide, or an alkali metal or an ammonium persulphate, etc., may be employed. Any of the well-known emulsifying agents capable of forming stable acidic emulsions may be used in preparing the emulsion. Nopco (a sodium salt of sulphonated sperm oil) is preferred.

The polymerization is carried out by heating the emulsion in a closed container at temperatures between 50 and 150 C., preferably between 60 and 100 C., until the polymerization is largely, but not entirely, complete, e. g. until from 80 to 95 per cent by weight of the polymerizable compounds have reacted. Usually from 15 minutes to 1 hour of heating are sufficient to complete the polymerization to this point. The progress of the polymerization reaction may be followed by observing the vapor pressure of the reaction mixture. It is important that the reaction be stopped slightly short of completion, since the final 5 per cent or so of the diolefine, if polymerized, may render the product nontacky.

It should be mentioned that when employing this combination of reaction conditions, the tackiness of the product tends to increase with increase in the iron salt content of the emulsion.

4 However, when the proportion of the iron salt is increased, e. g. above 200 parts by weight of iron per million parts of the polymerizable compounds, the rate of decomposition of the peroxide becomes 5 quite rapid and it becomes increasingly difficult to maintain a peroxide in the emulsion through- :out the polymerization reaction. For these reasons, the iron salt is usually employed in a proportion such as to contain from to 100 parts by weight of iron per million parts of the compounds to be polymerized, but it may be used in smaller or in larger porportions.

The tacky type of co-polymer and the nontacky co-polymer are mixed in proportions such that the resulting mixture contains from 5 to 25, preferably from 8 to 20, per cent by Weight of the tacky co-polymer, based on the combined weight of these ingredients. The mixing may be accomplished in any of the usual ways, e. g. by mixing the aqueous emulsions of the two types of copolymers and simultaneously coagulating the co,- polymers from the resultant mixture, or by separately coagulating each type of co-polymer from the emulsion in which it is formed and thoroughly mixing the co-polymers on compounding rolls or in other ways.. In either case a small proportion, e. g. 0.5 to 2 per cent, of a rubber antioxidant, such as phenyl-beta-naphthylamine, di-(p-hydroxy-phenyl) -cyclohexane, Antox (i. e. a condensation product of aniline, and butyraldehyde), or Thermofiex (i.v e, p.p'-dimethoxy-di phenylamine) etc., may advantageously be added to the emulsion, or emulsions, prior to coagulating the co-polymers so as to protect the latter against oxidation by air.

The tacky rubber-like mixture of co-polymers when compounded with usual rubber-compounding agents, e. g. carbon black, sulphur, anti-oxidants, vulcanization accelerators, plasticizing 0 agents, fillers, etc., produces a tacky mixture suitable for curing. However, upon curing the latter mixture, a non-tacky rubbery final product is obtained. The vulcanized final product possesses good mechanical properties such as a high 5 tensile strength, a high per cent elongation value, good elasticity and excellent resistance to wear by abrasion. Prior to, or during, vulcanization of the'product, i. e. whil it is in the tacky condition, it may be applied in any of the usual ways to 50 fabrics of cotton, rayon, or other materials, to obtain a good bond. After being vulcanized, the rubber-like product, which no longer is tacky, remains firmly bonded to the fabric.

The following examples illustrate certain ways 55 in which the principle of the invention has been applied, but are not to be construed as limiting its scope.

EXAMPLE 1 An aqueous emulsion was prepared which contained 120 grams of butadiene-1.3, 120 grams of methyl isopropenyl ketone, 60 grams of styrene,

2.5 kilograms of water, 30 grams of Nopco (a sodium salt of sulphonated sperm oil), 7.8 gramsof hydrogen peroxide (H202), 0.1 gram of ferric nitrate, Fe(NOs)3-9H2O, i. e. an amount of ferric nitrate corresponding to 46 parts by weight of iron per million parts of the polymerizable .compounds, and sufficient nitric acid to give the emulsion a pH value of 2. The emulsion was heated with agitation in a closed container at C. for 18 minutes, at the end of which time about 90 per cent of the mixture of butadiene, methyl isopropenyl ketone and styren initially employed had been polymerized. The product. was coagu- 7 lated by adding sodium chloride to the emulsion,

The product thus precipitated was separated from the liquor, washed with water and dried by warming the same at about 60 C. under vacuum. It is an extremely tacky soft solid which is capable of flowing gradually on long standing. It is capable of being elongated considerably before breaking, is somewhat though not highly elastic, and is readily soluble in cyclohexanone. It is capable of being vulcanized to form a non-tacky,

6 canized to form a firm bond with the latter. The compounded material was rolled into a sheet and cured by heating under pressure at 148 C. for 20 minutes. Standard test strips out from the cured sheets were used to determine the tensile strength and the per cent elongation proportion of the products, as described in A. S. T. M. D412-39T and also to determine the Shore durometer hardness. These properties of the compounded and elastic rubbery material. 10 cured products are also given in the table.

Table I (lo-polymers mixed Properties of cured product R N Uncuregl un Percent Percent gg g e Tensile Percent Quittin c fifftr itiffstiit. elongation Hardness 1 .i o 100 Non-tacky.. 2,660 430 60 2 9 91 Tacky 2,400 510 56 3 17 83 Verytacky. 2,550 570 50 4 23 77 Slightly 1,420 390 56 tacky.

EXAMPLE 2 It will be noted that the addition to the nontacky type of co-polymer of the tacky type of 3.2 parts by weight of butad1ene-1.3, 3.2 parts of methyl e m and parts tft e fsttitf 355523251; i fct iiriot t rene .were admlxedf Wlth parts Of-an aqueous impair any of the physical properties of the mass solution of Aliphatic Ester Sulphate (1. e. 011 ester Whe com ounded and ured d that it sulphate) and 8.5 parts of an'aqueous solution cergam of th 8 g However 3; which contained 1 per cent by weight of Aquarex 3 of as much as s 0 the tacky'type D mono-506mm sulphate-i811 of mlx of co-polymer did not result in the formation of ture of higher fatty alcohols, principally lauryl a satisfactorfl tack mass and did 8 k the and myristic alcohols), 1 per cent of Santomerse roduct obtainid b g ounding g fi i the 3 an alkali metalsalt lass For these r eason s we employ not i nore sulphonate) a 9 sodluml g than 25 per cent, and preferably from 8 to 20 per i per 0 p0 355mm cent, of the tacky type of copolymer together with mixture was agitated to effect emulsification and th ommck t f 1 the emulsion was heated with agitation in a closed e n y ype o ymer' container at 60 C. for approximately 20 hours, EXAMPLE 4 e y Polymerization Was effected- 9 40 A series of experiments similar to those detainel Was then Opened and W polymenza'tlon scribed in Example 3 were carried out, except product was coagulaited by addmg an aqueous that the non-tacky type of co-polymer employed cillm Chloride solutlon- The P was sepa in these experiments was a copolymer of butarated from the liquor, washed with water and dime methyl isopropenyl ketone and Styrene in dried under Vacuum The Product 15 a the proportions of approximately 40 per cent by tacky rubbery Substance Whlch may be weight of butadiene, 30 per cent of methyl iso- Dounded with usual rubber-compoun agents, propenyl ketone and 30 per cent of styrene. e. g. carbon black, sulphur, etc., and cured to ob- The tacky type of co polym r was prepared as tain a vulcanized rubbery product having good described in Example The mixture of copo1y mechanical properties, e. g. high tensile'strength mers was compounded as in Example Table H and elasticity, and possessing exceptional resistgives the per cent by Weight of the vtacky type of ance to wear by abras1on. co-polymer in the mixture of the same with the EXAMPLE 3 non-tackcy1 13 p; otf co-polymer,states whether the compoun e u uncured, mass was tacky, and each of senes expenments 100 P gives the tensile strength, the per cent elonga- Welght of the unvulca'mzed p rubber'hke tion value and the Shore durometer hardness of prfepared as m .Example 2 were the product after it was compounded and cured treated with different proportions of the tacky, as in Example 3 cyclohexanone-soluble co-polymer product of Example 1 and with 40 parts of carbon black, 5 parts Table II of zinc oxide, 2 parts of sulphur, 1 part of mercapto-benzothiazole, 1 part of stearic acid, and 20 Cured product parts of dibutyl sebacate and the resultant mix- Run Perce t of Uneured ture was worked on compounding rolls until suboutfitter ith? Tensile Percent ar stantially homogeneous. In the following table, lg fs l f g elongation ness the proportion of the tacky type of co-polymer used in the mixture is expressed as per cent of 9 2,920 450 62 the combined weight of the two co-polymers. 17 .d o 2,220 490 60 The resultant mixture was examined for tacki- 23 1 56 mess, the test being to press two pieces, of such mass together in the hands and then pull them EXAMPLE 5 apart. If the pieces pressed together adhered tightly and resisted separation they were regarded as tacky. The tacky masses may be pressed or worked onto a cotton fabric and vulthat the non-tacky type of copolymer was composed of 50 per cent by weight of butadiene, 45

cent of styrene. :weight-of the tacky co-polymer product of Example 1, based on the combined weight of the tacky and the non-tacky copolymers, in the compounded mass, states whether the compounded, but uncured mass was tacky, and gives the tensile strength, the per cent elongation value and the Shore durometer hardness of the compounded Other modes of applying the principle of the invention may be employed instead of those described, change being made as regards the method or compositions herein disclosed, provided the steps or ingredients stated by any of the following claims or the equivalent of such stated step or steps be employed. I a

We therefore particularly point out and distinctly claim as our invention:

1.- A tacky rubber-like composition comprising from '75 to 95 per cent by weight of a non-tacky rubber-like co-polymer and from to per cent of a tacky, cyclohexanone-soluble co-polymer, based on the combined weight of the co-polymers, each of which co-polymers is composed, in chemically combined form, of from 3'7 to 65 per cent of an aliphatic conjugated diolefine, from 1 to per cent of a 2-aryl-1-alkene, and from 20 to 60 per cent of an unsaturated ketone having the general formula:

a pH value below 3 and which contains an iron.

salt and a peroxide, and the non-tacky rubberlike co-polymer component of the composition being one prepared by co-polymerizingtlie corresponding polymerizable monomeric compounds under conditions other than those just specified for formation of the tacky co-polymer component. 2. A tacky rubber-1ike composition comprising from 80 to 92 per cent by weight of a non-tacky rubber-like co -polymer and from 8 to 20 per cent of a tacky, cyclohexanone-soluble co-polymer, based on the combined weight of the co-polymers, each of which co-polymers is composed, in chemically combined form, of from 3'? to 65 per cent of butadiene-1.3, from 1 to 30 per cent of a 2-aryl-1- cncnm C000 alkene, and from 20 to 60 per cent of an unsaturated ketone having the general formula:

wherein R represents an alkyl radical and R. represents a member of the group consisting of hydrogen and alkyl radicals, the above-mentioned tacky cyclohexanone-soluble co-polymer being one formed by co-polymerizing the corresponding polymerizable monomeric compounds while in an aqueous emulsion thereof which is of a pH value below 3 and which contains an iron salt and a peroxide, and the non-tacky rubber-like co-polymer component of the composition being one prepared by co-polymerizing the corresponding polymerizable monomeric compounds under conditions other than those just specified for formation of the tacky co-polymer component.

3. A tacky rubber-like composition comprising from 80 to 92 per cent by weight of a non-tacky rubber-like co-polymer and from 8 to 20 per cent of a tacky, cyclohexanone-soluble co-polymer, based on the combined weight of .the co-polymers, each of which co-polymersis composed, in chemically combined form, of from 37 to per cent of butadiene-lB, from 1 to 30 per cent of a 2-aryl-lalkene, and from 20 to 60 per cent of methyl isopropenyl ketone, the above mentioned tacky 'cyclohexanone-soluble co-polymer being I one formed by co-polymerizing the corresponding polymerizable monomericcompounds while in an aqueous emulsion thereof which is of a pH value below 3 and which contains an iron salt and a peroxide, and the non-tacky rubber-like co-polymer component of the composition being one prepared by copolymerizing the corresponding polymerizable monomeric compounds under conditions other than those just specified for formation of the tacky copolymer component.

4. A tacky rubber-like composition comprising from to 92 per cent by weight of a non-tacky rubber-like co-polymer and from 8 to 20 per cent of a tacky, cyclohexanone-soluble co-polymer, based on the combined weight of the co-polymers, each of which co-polymers is composed, in chemically combined form, of from 3'7 to 65 per cent of butadiene-1.3, from.1 to 30 per cent of styrene, and from 20 to 60 per cent of methyl isopropenyl ketone, the above-mentioned tacky cyclohexanone-soluble co-polymer' being one formed by co-polymerizing the corresponding polymerizable monomeric compounds while in an aqueous emulsion thereof which is'of a pH value below 3 and which contains an iron salt and a peroxide, and

the non-tacky rubber-like co-polymer component ofthe composition being one prepared by copolyrnerizing the corresponding polymerizable monomeric compounds under conditions other 'thanthose just specified for formation of the 

